Electromagnetic switch.



E.;R. CARICHOFFI EL ECTRbMAGNETIC SWITCH.- ARPLICAHON men SEPT-25.1916.

I Patented Aug- 13, 19 -4 v Rm v Fig.3.

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T 0 all whom it may concern:

Be it known that I, EUGENE a citizen of the United States, residing'at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Electromagnetic Switches, of which the following is a specification.

My invention relates to electromagnetic switches for controlling electric circuits and more particularly to switches of this character which hold open when the current in a circuit is relatively and closed when the current drops to a'prdetermined value. In the starting of electric motors, it has been the practice to employ a plurality of electromagnetic switches which close successively to cut out sections of resistance from the motor circuit and bring the motor up to speed. Various means have been devised for controlling the operation of the switches so that they will only close when the current i has operated to cut out a section of resist this general character ance the next switch will not operate until. the current has dropped to a safe value due to the speeding up of the motor.

A form of switch which has frequently been proposed for this purpose is one-in which a shunt coil closes the switch and a series coil, instead of controlling the circuit of the shunt coil, positively prevents the switch from closing by actually holding it open, that is, the shunt coil pulls against the series or holding-out coil.

is disclosed in patent to Fraser, #655,335. The difiiculty with the device shown in this patent is that the value of current in the holding-outwinding at which the switch will close depends upon the pull of the shunt coil, which of course -will vary with the voltage and also with the temperature of the coil. In other words, the setting of the switch, 1'. e. the motor current value at which it closes, changes with change of voltage. It also closes at one value of current in the series coil when the shunt coil is cold and another when it is at its operating temperature which is ordinarily about degrees C.

Attempts have been made to overcome this difliculty by having an auxiliary which is operated by the shunt coil, place :a spring under tension which tends to move the switch member to closed position. This A switch of member.

Application filed September 25, 1916. Serial mfmsee drops to a predetermined value, the spring overcomes the pull of the series coil and closes the switch. Such an arrangement is is closed by a .spring instead of by electro-. magnetic pull, and it is impossible to obtain the required pressure between the contacts. The spring weakens as the switch member moves toward closed'position, and the press ing together of the contacts is accomplished when the spring is weakest. .Asthe-p'a'rts wear, the pressure between the contacts decreases. i l One of the objects of my invention is to improve the electromagnetic switch of the type above described by providing means whereby the switch member will be operated so as to be positively closed and wiped home by the electromagneticpull ofthe shunt'coil Specification of Letters Patent. Pat nt d "tendency .is opposed by the series coilwhenj R. CAn1crrom- ,f1 th current is high andwhen the current 00' unsatisfactory for the reason that the switch.

when the current in the series coil drops to a predetermined value, thisbeing accomplishedby the use of an auxiliary member which is moved by the shunt coil to give the switch member a bias or tendency to'close,

series coil. The result of this. arrangement is that the value of current in the series coil which bias or tendency is opposed by the side elevation of a complete electromagnetic switch embodying my improvements; Fig. 2 is a front elevation of the same; and Figs. 3, 4 and 5 show in outline the various po sitions which the switch assumes in operation. Y 1 1 Referring to Figs. 1 and 2, 10 represents an energizing winding which is shown-as a. fine wire winding suitable for use as a shunt winding on an electromagnetic switch'for cont-rolling motor circuits. This windingis arranged to energize the magnetic structure composed of an upper pole piece 11 anda lower pole piece 12 connected-by core 13. These parts, together with the winding 10 mounted upon the core, form an electromagnet which is secured to an insulating base ll. A fixed contact 15 is also secured to the insulating base adjacent the magnet so as to pivoted at 17 to the magnet frame; For

the fixed contact 15.

cooperate with the moving contact as hereinafter described. A switch member 16 1S this purpose a bracket 18, preferably of brass or other non-magnetic material, is secured to the pole piece .11. T1118 bracket has arms 19extend1ng downward and outward from bracket 21 pivoted at 22, there being a compression spring 23 interposed between the bracket and a projecting lug 2-1 on the switch member 16. A tail piece 25 is provided for the bracket 21 for limiting the movement of the bracket in.resp'onse to the pressure of spring 23. The. lower end of the switch member forms ,an armature 26 which cooperates with the pole piece 12 and also with an auxiliary pole piece 27 which is secured to the pole piece 12 and bent around. as shown, so that the magnetic circuit through "the auxiliary pole piece is longer than that through the pole piece 12'. 'T-he-end of the switch member moves freely between the two pole pieces. The switch member, with the parts attached thereto, is so pivoted and Weighted that it normally assumes the position shown in Fig. 1, that is, it is biased switch member, is a lever 29 of magnetic;

to the open position with the lower end separated from, the pole piece 12 by the space 28.

Pivoted on the pivot 17 of the switch member, so as to move independently of the material. The upper end of this lever cooperates with the pole piece 11 so as to be magnetically attracted thereby while the lower end projects into the switch member .16, that is, it entersthe space formed by the two webs of the member etween the lower end of this lever 29 and the switch member proper is interposed a spring 30 which abuts againts the adjusting screw 31. The arrangement is such that when the lever 29 is attracted by the pole piece 11 and the switch member 16 is held in its normal position shown in the drawing, the spring 30 is compressed so as to give the switch member 16 a tendency to rotate on its pivot and bring the contact 20 into engagement with contact 15. his tendency to move the switch member is increased by the. magnetic attraction betwen the lower end of the switch member and the auxiliary pole piece 27.

The arrangement thus far described is substantially the same as that disclosed in my previous application, Serial Ne. 870,807, filed Nov. 17, 1914:, the principal distinction being, that while in my previous application the switch member in its normal position rests against the pole piece .-12 with a nonmagnetic stop interposed, in the present case, the member normally rests against a magnetic pole Piece energized bythe holding-out winding. It will be seen, therefore, that the switch ot'niy previous-application may be utilized either as a single winding contactor of the look-out type, or,'by the addition of the parts hereinafter described, may be utilized as a compound contactor, that is, one havinga shunt operating winding and a series holding-out winding.

Secured to the insulating base below the magnetic structure just described is an electrom-agnet comprising a U-shaped pole piece in'closing a magnetizing winding 33. This winding it will be observed is a heavy or coarse winding of a type suitable for carrying the motor current Where the switch is used for controlling an electric motor; This winding is shown as being divided into two parts, this being for the purpose of strongly holding the switch member in open position with a large number of turns until it is desired that the switch shall be under the control of the motor current whereupon a part of the turns will be cut out. Secured to the lower end of the switch member 16 by screws 3%, is an arm which projects downward toward the pole piece Secured to the lower end of this arm is an 100 armature 36 which cooperates with the pole piece 32. This armature is adjustable upon. the arm 35 by means of a screw 37, the armature having a knurled edge engaged by a, latching member 38, which holds the arma- 105 ture in any position to which it may be turned. By means of the screw 37 the armature 26 may be so positioned that it is equally attracted by the pole piece on either side of it so that the magnetic forces acting 110 on either side of the armature 26 are substantially balanced. hen the winding 33 is suiiiciently energized, the pole piece 32 attracts the armature 36 and thusholds the switch inember in open position.

As thus constructed and arranged, the operation of this switch is as follows: Assuming that the winding 10 is energized by being connected across a circuit which is of substantially constant potential, and the 120 winding 33, either as a whole or in part. connected to a circuit in whichthe current is variable, as for instance in the armature circuitof an electric'motor, if the current in the circuit to which this winding is connect 125 ed is of such a value that the switch should not close, the switch member will be held open and the-parts will assume the position shown in Fig. i. It will be noted by reference' to Figs. 1 and 3 that the only thing that 130 i erases has happened, that is, theonly; part that has moved iS-the lever 29 which has moved up to the pole piece'll due to the energization of the winding 10, and has compressed the spring 30. The tension of this spring now gives the switch membera tendency to close,

which tendency is opposed by the pole piece of the pole piece 27 varies due to variations tion of the winding 33. There is also a pull across the gapQS which, however, is of no importance in' this connection sincev the-gap is so adjusted that the tension of the spring, together with the pullof the auxiliary pole piece 27, will preponderate and cause the switch to close when the current'in'the winding 33 drops to a predetermined value. The value of current at which thes'witchwill close may be adjusted by adjusting the armature 36 on its's'crew so as to vary the air gap between it and the pole piece 32. W hen the current in thewinding 32 drops to the predetermined .value, at whichit is desired that the switch shall close, the constant force due to the tension of the spring 30, together with the magnetic pull of the pole piece 27,

which will vary somewhat due to the. variathe coil 10, and the pull 1 of the pole piece 32, and the switch parts tions in voltage upon heating. of the cell will overcome the wili move to the position shownin Fig. 5. It will be noted, however, that while the pull in voltage and heatingofthe coil 10, this variation will not substantially vary the point at which the switch will close, because it is offset by variations in pull across the air gap 28, since the pull in these two air gaps varies at the same rate. force which tends to move the switch toward closed position therefore, will be substantially. the constant force of the spring tending'toclose the switch opposed by the vari-- able magnetic force due to the winding 33. The switch will, therefore, always close at a definite value'of current in the windlng 33 regardless of any variations of magnetizing force due to the winding 10.

While I have described my invention as QIHbOCli d -il'icOllClGtB form and as operatlng in aspecifie manner in accordance with the provisions of the patent statutes, it should be understood that my invention is not limited thereto, since various modifications thereof will suggest themselves skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What Iclaim' as new and desire to secure by Letters Patent of the United States, is

1. An electromagnetic switch comprising an energizing winding and a magnetic structure therefor, a switch arm normally in open,- position and held in closed position by a' direct magnetic pull thereon set up by said winding, a member moved by the said windto a predetermined value. 32, the pull of whichfis dueto the energizature therefor, aswitch arm nor 57a direct magnetic pull thereon;

to apply 'a constant force tendin to mbive ,f

The effective to those 71 drops An electromagnetic.switc an energizing w nding and amag ,V

position andgheld, in close direct magueticpull ther 'eons a winding, a holding-oiitfwindin an H H her moved by the-energizing u ,ndin'g r a constant force,'wh"ch reacts on ,'th'e 1s Tjitch arm to move it in a closing direction en the current in said windi lrops,to", determined value. *3. An electron'iagnetic',sw tc g an energizing winding anda, magnetic -r uc- 3,5

ture therefor, a switch arn open positionand held in close winding, a member movedbi th the switch arm to closed positi oiit ianda holding-out winding for holding the .swi ch arm in open position nntilgthegfcurrent ,in said' holdin'g out winding drops to a predetermined value. l

4. An electromagnetic switch comprising an energiz'ing winding and a magnetic strucs ture therefor, a switch arm normally in open position and held in closed position by a direct magnetic pull thereon set up by said winding, a member moved by thewinding to apply a constant force to said switch arm in a direction to closeth'e switch arm, and a holding-out winding for holding the switcharm against thevconstant force until the; current in 'saidholding-out winding drops to a predetermined value.

5. 'An electromagnetic switch comprising Ian-energizing winding and a magnetic by said windingactin onone side of the pivot, a holding-out winding acting on the .sanie side of the pivot to hold the switch arm in open position, and a member moved by the energizing winding to set up a force which becomes effective to move the switch member in a closing direction when the current in the hoiding-out winding drops to a predetermined value.

6. An electromagnetic switch comprising an energizing winding and a magnetic structure therefor, a pivoted switch arm normally in open position and held in closed position by a magnetic force set up by said winding acting on one sideof the pivot, a holding-out wii'iding acting on the same'side of the pivot to hold the switch arm in open position, and a member moved by the magnetic force of said energizing winding acting on the other sideof the pivot'to set up a constant force which becomes effective to move the switch member in a closing direction when the current in the holding-out winding drops to a predetermined value.

7. An electromagnetic switch comprising an energizing winding and a magnetic structure therefor, a switch -arm normally in open position and acted upon by a force set up by said winding tending to move it to closed position and a counteracting force set up by said winding which substantially balances the arm magnetically, a holding-out winding for holding the switch arm in open position, and a member moved by the energizing winding against a constant force which reacts on the switch arm to move it out of balanceso that the closing force prevails to close the switch when the current in the holding-out Winding drops to a predetermined value.

8. An electromagnetic switch comprising an energizing winding and a magnetic structure therefor, a switch arm normally in open position and held in closed position by a direct magnetic-pull thereon set up by said -winding, a spring a member moved by said winding to place said spring under strain and set up a force in a direction to move the switch arm to closed position and 9. holding-out winding for preventing the force from becoming effective to move the switch arm in a closing direction until the current in. saidholding-out winding drops to a predetermined value.

9. An electromagnetic switch comprising an energizing winding and a magnetic struc ture therefor, a switch arm normally in open v 'position and acted upon by a force set up by said winding'tending to move it to closed when the current in the holding-out winding drops to a predetermined value.

In witness whereof, I have hereunto set my hand this 23rd day of September, 1916.

EUGENE R. OARICHOF F. 

